A mobile terminal may have multiple interfaces allowing it to connect over multiple link layers (L2s) to different access networks.
Some access networks are likely to be preferred to others, as they provide higher bandwidths, a lower latency, a better support for fast moving terminals or lower costs. For instance, a Wireless Local Area Network (WLAN) is not designed for moving terminals at all, albeit slow movements of the terminals are possible and can be handled, whereas cellular systems are designed to be also used for providing communication with fast moving terminals such as terminals used in cars and trains. On the other hand, all access networks are not available in every geographical location.
If a mobile terminal moves from a location covered only by a wide-area access network, e.g. a cellular network, into a location that is also covered by a local-area access network, e.g. a WLAN, the mobile terminal may want to take a decision on whether to continue to use the wide-area access network or make a handoff to the local-area access network.
Existing work in regard of multi-access has been directed to devising different methods for detecting network topological movement and the access network/method to prefer.
Existing work in regard of detecting geographical information has been focused on how to determine the absolute position of a mobile terminal, in order to enable positioning services or localizing services.
Existing work in regard of improving access selection in the Network/IP (Internet Protocol) layer L3 using information collected on the physical layer, L1, and on the link layer, L2, has been very limited as to the implementation. Cellular links are usually represented as point-to-point (PPP) links, where the entire nature of the physical radio communication is hidden from the network layer L3. WLAN links are only represented as Ethernet links, in which the only information propagated upwards is “link up/down”. Of course, the network layer L3 should generally be unaware of the detailed characteristics of the link, i.e. of the exact transfer of information, but a management mechanism on the network layer L3, such as an access selection mechanism/function, should still be aware of the dynamics of data transmission over the links.
Work has been done in regard of using speed-estimation and fuzzy logic in order to aid handoff decisions between hybrid networks such as combined cellular and WLAN networks. The disclosed hand-off decisions are used in mobile terminals or choosing en access network/access method that can handle the speed with which the mobile terminals are moving.
Problems Associated with Existing Solutions
A handoff such as described above from a cellular network to a WLAN may require some time, such as a time period of the magnitude of order of 1-10 seconds, to be completed in the case where mobility mechanisms based on the IP-layer are used.
If the mobile terminal is geographically quickly moving out of the area covered by the WLAN it will not make any sense to try to handoff into it in the first place, only to then have to handoff out of it again a few seconds later.
Likewise, if the mobile terminal is geographically located in an area covered by an access network, which is lacking radio and network support for quickly moving mobile terminals/nodes, and the mobile terminal is moved into a vehicle, e.g. a bus, a car, or a train, that starts to move with a speed which would have serious impact on ongoing communication services, it would be useful for the mobile terminal to handoff to a radio access technology that is more appropriate for fast moving terminals.
It is important that the mobile terminal should use an access network/method that is designed for the speed with which the mobile terminal is moving.
Generally, a handoff may incur loss of packets, that packets are received out of order or a large variation of latency and should be considered well before being performed.
Topological Movement Detection
Detection of movement of a mobile terminal in the network topology is required to make handoffs on the network layer, L3. However, a detected movement in the network topology does not include a measure of the time during which the mobile terminal can be predicted to stay in the same subnet or to be connected to the same point of attachment, as there is no information on or estimation of the speed of the physical/geographical movement of the mobile terminal.
The existing work has focused on trying to minimize handoff effects or handoff duration. Most of the existing work has not been helpful in providing input to an access selection process on the anticipated time period during which the mobile terminal will stay in a particular cell, or to provide input to access selection that has to select between different types of access networks, where there is no coordination or cooperation between the cells or access networks of different types.
Positioning/Localizing
The existing work on positioning mobile terminals, also called localizing mobile terminals, has focused on how to determine the absolute, geographical positions of the mobile terminals, the work based on one or multiple cells belonging to one or multiple access networks. Thus, the existing work primarily deals with the problem of determining the position of mobile terminals, this problem generally being more complex than determining of only the geographical speeds of the mobile terminals.
A procedure and possible associated devices that can measure the absolute geographical position of a mobile terminal can obviously also be easily modified to also calculate the geographical speed of the mobile terminal. A problem associated with such a modification is that positioning or localizing procedures already are quite complex and that they already require a high level of calculations from the mobile terminal and/or information about the infrastructure, such as information on existing roads in a cell.
Information from Lower Layers to Network Layer L3
In existing implementations there is no common way for different lower layers to convey to higher layers any kind of information about the way in which the dynamic radio conditions change over time.
The general case is that lower layers express no information at all to higher layers, except information on the up/down status of links.
Most implementations of lower layers have their functionality split between a driver, i.e. a software program, and firmware/hardware. Whereas the firmware/hardware has detailed information about physical parameters such as signal strength, such information is not exposed upwards in the layer structure at all. When it is exposed, the difference as to the implementations varies enormously. Hence, there is no way for a procedure that is performed in the network layer L3 is independent of lower layers, such as an access selection procedure, to know where to read such information, if it can be read at all.
Coordinated Access Networks
Some of the current procedures for positioning a mobile terminal generally require that the mobile terminal is aware of some level of the geographical topology of the access network to which is connected.
Some of the current procedures for handling handoffs for a mobile terminal moving between different types of access networks require that there is some coordination or cooperation between the access networks. However, such coordination or cooperation may be a too complex requirement for a method in which the mobile terminal at each time instance is selecting a good or best access network.
Problems Associated with Existing Speed-Estimation Solutions
The solution and algorithm presented in the article for Majlesi et al. cited above does not point out how speed estimation is actually performed, but references e.g. Doppler frequency speed estimation proposals, that current hardware does not provide. A mathematically complicated algorithm for estimation of speed in a cellular network is disclosed in the cited article for Austin et al. This prior algorithm has to be executed in a base station.
Furthermore, the algorithm proposed in the cited article for Majlesi et al. is explicitly designed for hybrid networks consisting of combined cellular networks and WLANs. It cannot handle different lower layers in a generic manner, but is hardcoded with information about the two lower layers, i.e. about the cellular networks and the WLANs.
The previously disclosed algorithm does not open up for a combination of input from different decision-taking entities within a mobile terminal, such as applications, operator policies, or user preferences.